A thin circuit board (blade) mounted with such elements as a central processing unit (CPU), a memory, a hard disk, and a network controller, which are necessary for operating as a server, is called a server blade. Further, a system in which a plurality of server blades are mounted within a chassis serving as an enclosure, and are operated as one server is called a blade server.
With the server blades sharing the power supply and the management unit, the blade server get to mounting the server blades in high density and low power consumption. When the throughput is increased, the blade server can adapt the increase of the throughput just by installing additional server blades. For this reason, the blade server is superior in expandability.
Along with the installation of additional server blades, there may occur a case in which the storage capacity including the hard disk needs to be expanded. Conventionally, this has been handled by providing a storage box separately from the blade server. However, due to increasing demand for all-in-one blade servers, it is desired that the storage blade be mounted within the blade server.
Those blades constituting the blade server are mounted in the chassis via a so-called back plate. The installation of a blade to the chassis is performed by inserting the blade into a connector provided on the back plate installed inside the chassis. With this, the blade can be connected, without using a cable, to such modules as a network switch and a power supply, which are provided to the blade server.
Incidentally, as one of the arrangements for connection methods between computer main bodies and peripheral devices, a small computer system interface (SCSI) is conventionally known. Further, there exists a new standard, a serial attached SCSI (SAS), which is one type of the SCSI standards, and is capable of serial communication owing to adoption of a serial ATA (SATA) interface.
With the SCSI standards, as a data transfer method, there is adopted a parallel transfer method in which a plurality of pieces of data are transferred in parallel through a plurality of communication lines. However, with the SCSI standards, due to the fact that a large number of data signals are transferred simultaneously, slight differences in transmission speed occur among the signals. With SAS, such differences are eliminated by high-speed serial transfer, getting to transfer with high accuracy.
For this reason, the trend for the storage interface has been to shift from the SCSI interface to the SAS interface. In addition, server blades of a new generation (new-generation server blades), which are capable of storage expansion using the SAS interface, have been developed. Therefore, it is believed that, in the future, the conventional server blades (previous-generation server blades) are replaced by the use of the new-generation server blades.    [Patent document 1] JP 2006-235964 A    [Patent document 2] JP 2007-213584 A    [Patent document 3] JP 2008-9648 A
As described above, in a system in which an information processing unit like a server blade and a storage unit like a storage blade are connected through an interface, when the conventional interface is replaced with a new interface, there arises a problem as to how to maintain compatibility.
Specifically, the conventional interface and the new interface have not only a difference in configuration but also various differences in function. For example, some interfaces execute a sequence in which, at power-on, the storage unit is powered on first, and then, the information processing unit is powered on. On the other hand, other interfaces do not execute such a sequence, and hence each unit needs to be powered on separately.